Buggy code:
public class Renderer implements ExprVisitor , RenderingContext , StatementVisitor { private static final String variableNames = "abcdefghijkmnopqrstuvwxyz" ; private static final String variablePartNames = "abcdefghijkmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789" ; private NamingStrategy naming ; private SourceWriter writer ; private ListableClassHolderSource classSource ; private ClassLoader classLoader ; private boolean minifying ; private Map < MethodReference , Renderer . InjectorHolder > injectorMap = new HashMap < > ( ) ; private Map < String , Integer > stringPoolMap = new HashMap < > ( ) ; private List < String > stringPool = new ArrayList < > ( ) ; private Properties properties = new Properties ( ) ; private ServiceRepository services ; private DebugInformationEmitter debugEmitter = new DummyDebugInformationEmitter ( ) ; private Deque < Renderer . LocationStackEntry > locationStack = new ArrayDeque < > ( ) ; private DeferredCallSite lastCallSite ; private DeferredCallSite prevCallSite ; private Set < MethodReference > asyncMethods ; private Set < MethodReference > asyncFamilyMethods ; private Diagnostics diagnostics ; private boolean async ; private Priority priority ; private Associativity associativity ; private boolean wasGrouped ; private Deque < Renderer . OperatorPrecedence > precedenceStack = new ArrayDeque < > ( ) ; private Map < String , String > blockIdMap = new HashMap < > ( ) ; private static class OperatorPrecedence { Priority priority ; Associativity associativity ; boolean wasGrouped ; } @ Override public void visit ( MonitorEnterStatement statement ) { try { MethodReference monitorEnterRef = new MethodReference ( Object . class , "monitorEnter" , Object . class , void . class ) ; <START_BUG> writer . appendMethodBody ( monitorEnterRef ) . append ( "(" ) ; <END_BUG> statement . getObjectRef ( ) . acceptVisitor ( this ) ; writer . append ( "," ) . ws ( ) ; writer . append ( "$rt_continue($part_" ) . append ( statement . getAsyncTarget ( ) ) . append ( ')' ) ; writer . append ( ");" ) . softNewLine ( ) ; } catch ( IOException ex ) { throw new RenderingException ( "IO<seq2seq4repair_space>error<seq2seq4repair_space>occured" , ex ) ; } } @ Override public void visit ( MonitorExitStatement statement ) { } private static class InjectorHolder { public final Injector injector ; public InjectorHolder ( Injector injector ) { } } private static class LocationStackEntry { NodeLocation location ; public LocationStackEntry ( NodeLocation location ) { } } public void addInjector ( MethodReference method , Injector injector ) { } public Renderer ( SourceWriter writer , ListableClassHolderSource classSource , ClassLoader classLoader , ServiceRepository services , Set < MethodReference > asyncMethods , Set < MethodReference > asyncFamilyMethods , Diagnostics diagnostics ) { } @ Override public SourceWriter getWriter ( ) { } @ Override public NamingStrategy getNaming ( ) { } @ Override public boolean isMinifying ( ) { } public void setMinifying ( boolean minifying ) { } @ Override public ListableClassHolderSource getClassSource ( ) { } @ Override public ClassLoader getClassLoader ( ) { } @ Override public Properties getProperties ( ) { } public DebugInformationEmitter getDebugEmitter ( ) { } public void setDebugEmitter ( DebugInformationEmitter debugEmitter ) { } public void setProperties ( Properties properties ) { } public void renderStringPool ( ) throws RenderingException { } public void renderRuntime ( ) throws RenderingException { } private void renderRuntimeCls ( ) throws IOException { } private void renderRuntimeString ( ) throws IOException { } private void renderRuntimeUnwrapString ( ) throws IOException { } private void renderRuntimeNullCheck ( ) throws IOException { } private void renderRuntimeIntern ( ) throws IOException { } private void renderRuntimeObjcls ( ) throws IOException { } private void renderRuntimeThreads ( ) throws IOException { } public void render ( List < ClassNode > classes ) throws RenderingException { } private void renderDeclaration ( ClassNode cls ) throws RenderingException { } private void renderMethodBodies ( ClassNode cls ) throws RenderingException { } private void renderClassMetadata ( List < ClassNode > classes ) { } private static Object getDefaultValue ( ValueType type ) { } private void renderInitializer ( MethodNode method ) throws IOException { } private void renderVirtualDeclarations ( List < MethodNode > methods ) throws IOException , NamingException { } public void renderBody ( MethodNode method , boolean inner ) throws IOException { } private class MethodBodyRenderer implements MethodNodeVisitor , GeneratorContext { private boolean async ; @ Override public void visit ( NativeMethodNode methodNode ) { } @ Override public void visit ( RegularMethodNode method ) { } @ Override public void visit ( AsyncMethodNode methodNode ) { } @ Override public String getParameterName ( int index ) { } @ Override public ListableClassReaderSource getClassSource ( ) { } @ Override public ClassLoader getClassLoader ( ) { } @ Override public Properties getProperties ( ) { } @ Override public < T > T getService ( Class < T > type ) { } @ Override public boolean isAsync ( ) { } @ Override public boolean isAsync ( MethodReference method ) { } @ Override public String getCompleteContinuation ( ) { } @ Override public Diagnostics getDiagnostics ( ) { } } private void pushLocation ( NodeLocation location ) { } private void popLocation ( ) { } @ Override public void visit ( AssignmentStatement statement ) throws RenderingException { } @ Override public void visit ( SequentialStatement statement ) { } @ Override public void visit ( ConditionalStatement statement ) { } @ Override public void visit ( SwitchStatement statement ) { } @ Override public void visit ( WhileStatement statement ) { } private String mapBlockId ( String id ) { } @ Override public void visit ( BlockStatement statement ) { } @ Override public void visit ( BreakStatement statement ) { } @ Override public void visit ( ContinueStatement statement ) { } @ Override public void visit ( ReturnStatement statement ) { } @ Override public void visit ( ThrowStatement statement ) { } @ Override public void visit ( InitClassStatement statement ) { } public String variableName ( int index ) { }

Fix:
writer . append ( "return<seq2seq4repair_space>" ) . appendMethodBody ( monitorEnterRef ) . append ( "(" ) ;